(1) Field of the Invention
The present invention relates to an anti-reflection optical article having excellent stain resistance, scratch resistance and processability and a process for the preparation of this optical article. More particularly, the present invention relates to an optical article which is valuably used as optical elements, for example, optical lenses such as spectacle lenses and camera lenses, and filters to be used as front plates of CRT (cathode ray tube) and Braun tubes to be used for CRT.
(2) Description of the Related Art
When an object is seen through a transparent material, if reflected rays are strong and a reflected image is clear, the ability to see is disturbed, and reflected images, such as so-called ghosts or flares, are formed to give an unpleasant feel to the eyes. Moreover, in the case of a looking glass, the content cannot be clearly seen because of rays reflected from the glass surface.
As means for preventing reflection, there has been adopted a method in which a substrate is covered with a material having a refractive index different from that of the substrate. It is known that in order to increase the reflection-preventing effect in this method, selection of the thickness of the substance covering the substrate is important. Namely, it is known that in the case of, for example, a single-layer coating, adjustment of the optical thickness of the substance having a refractive index lower than that of the substrate to 1/4 of the wavelength of the objective light or an odd number multiple thereof gives a minimum reflectance, that is, a maximum transmission.
The optical thickness referred to herein is given by a product of the refractive index of the coating-forming material and the thickness of the coating. An anti-reflection layer having a multi-layer structure can be formed, and several proposals have been made in connection with selection of the thickness of the coating layer [A. Vasicek, "Optics of Thin Films", 159-283, North-Holland Publishing Company, Amsterdam (1960)].
U.S. Pat. No. 4,361,598and U.S. Pat. Application Ser. No. 474,741, now abandoned, disclose a process in which a multi-layer anti-reflection film satisfying the above-mentioned optical thickness condition is formed by using a liquid composition.
In an anti-reflection film formed by the vacuum deposition method, the film-forming material is composed mainly of an inorganic oxide or inorganic halide, and essentially, the anti-reflection film has a high surface hardness, but it is readily stained with hand dirt, finger marks, sweat, hair liquid, hair spray and the like and it is difficult to remove these strains. Furthermore, since the surface slip is poor, thick scratches are readily formed. In addition, since the water wettability is large, if rain drops or water splashes adhere, water broadly spreads, and in case of a spectacle lens or the like, the observed object is seen distorted over a broad area.
In anti-reflection films disclosed in Japanese Unexamined Patent Publications No. 58-46301, No. 59-49501 and No. 59-50401, in order to impart a high surface hardness, it is necessary that an inorganic substance represented by fine particles of silica should be incorporated in an amount of at least 30% by weight in a topcoat layer. However, an anti-reflection film formed from such a film composition is poor in the surface slip and is readily scratched by rubbing with a cloth or the like.
Various surface treating agents have been proposed and marketed as means for eliminating these drawbacks, but since each of them is soluble in water or solvents, the function which is provided, is a temporary one and the durability is poor.
We made research with a view to solving the foregoing problems involved in the conventional techniques, and as the result, we have arrived at the present invention described hereinafter.